During operation of some agricultural machinery, crop residue is chopped up and deposited onto the ground rearward to the direction of travel of the machine. One example of such an arrangement is a straw chopping system of a combine harvester, in which straw is chopped and deposited in swathes rearwards to the direction of travel of the equipped vehicle, e.g. for later ploughing into the ground.
Some such agricultural machines, and in particular combine harvesters, work using a header attachment for gathering in crop. These header attachments, once deployed, may be significantly wider than the machine itself so as to achieve the widest crop collection window possible. By way of proportion, it is known by the applicants to provide a combine harvester of about 3 m wide with a header attachment having a width of cut from about 6 to 7 m depending on model, even approaching 10 meters in some cases.
If chopped straw is deposited rearwards in line with the combine body, it will form windrows or swathes that are similar in width to the body of the combine. Outboard of these swathes and up to the width of the header attachment, there are bare strips of ground. This gives rise to a number of problems, among which is the potential to disrupt even irrigation of the ground for at least the next crop generation. For example, if it rains before the swathes are worked into the ground and then the sun comes out, the deposited swathes will absorb water, which may evaporate in the sun and never reach the ground. There may also be other problems relating to uneven distribution in the ground of chopped crop residue after tilling. These and related problems may manifest themselves later by uneven crop growth in strips, which reduces efficiency of land use and is unsightly. Attempting to harvest in damp conditions or in rain only serves to exacerbate the problems, as the added weight of water in the chopped straw makes it fall down into ever more exaggerated narrow and piled up strips.
In order to try and alleviate these problems, various attempts have been made to distribute chopped straw more evenly across the window left behind by the width of cut of a combine header. One known approach is to provide a series of blades/guide vanes in the outlet of the straw chopper. These vanes may be angled to try and impart a spread to the exiting chopped straw.
One prior art straw chopper arrangement for combine harvesters is proposed in GB-2165732. In this arrangement, vanes are provided inside a discharge hood of a straw chopper mechanism in the form of guide plates. These guide plates are inclined outwardly towards their respective sides of the chopper hood with respect to the longitudinal axis of the combine. The guide plates are fixed in position in the hood that, among other things, may not be very efficient in windy conditions. With this arrangement, account cannot therefore be taken of wind causing drifting of the deposited chopped straw. In addition, the ends of the guide plates are substantially vertical and straw leaving such blades is projected in tunneled streams. While a potential improvement over arrangements having no guide plates, the streamed output may result in several smaller swathes behind the combine harvester and subsequently lead to diminished but nevertheless still present problems of stripes in one or more subsequent generations of crop.
In U.S. Pat. No. 6,331,142B1, a further prior art arrangement is disclosed having guide vanes curved in the vertical plane. These vanes again provide a predetermined trajectory to ejected chopped straw, while means are provided to move the vanes manually in order to change the configuration of the vanes so as to try and fan out the streams of straw across the width of the window left by the header. In this case, the outlet end of the guide vanes is inclined at an angle of approximately 45°, such that the straw that passes along the upper region of the blade leaves the blade later than that passing along the lower portions. As the straw leaves the blade tangentially in each region, the angle provided to the trailing edge of the guide blades allegedly produces a fanning effect to the exiting streams of straw in an attempt to more evenly distribute it over the ground behind the combine harvester. In the event of a side wind causing drifting of deposited chopped straw, it would be necessary to manually set the configuration of the vanes at the end of each pass across the crop gathering area, or to accept a serious compromise in efficiency.